1. Field of the Invention
The present invention relates to a method and device for preparing cleaning solutions.
2 Description of Related Art
The present inventors have already found that hydrogen water wherein a hydrogen gas is dissolved in deionized water and ozone water in which an ozone gas is dissolved in deionized water are effective for cleaning electronic parts such, for example, as semiconductor substrates, substrates used for liquid crystal displays and the like.
Generally, when a hydrogen gas or ozone gas is dissolved in deionized water, such a gas is dissolved under atmospheric pressure.
It is however, time-consuming, for a gas to reach a desired concentration when the gas is dissolved under atmospheric pressure.
What is worse, hydrogen or ozone water of sufficiently high concentrations cannot be obtained under this condition.
It is an object of the present invention to provide a method and device that can prepare highly-concentrated gas dissolved cleaning solutions in a short period of time.
It is another object of the present invention to provide a method and device for preparing cleaning solutions that have effective detergency and are easy to recycle by controlling the amount of a dissolved gas, thereby reducing the consumption of deionized water while recycling the waste cleaning solution.
An aspect of the present invention to carry out the aforementioned objects is a method for preparing cleaning solutions for cleaning objects to be cleaned such as an electronic parts member, comprising a step of dissolving any of an oxidative gas, reductive gas, inert gas, a mixture of an oxidative gas and an inert gas, or a mixture of a reductive gas and an inactive gas in deionized water while controlling the supply pressure of such a gas at a value exceeding the atmospheric pressure.
Electronic parts here can be exemplified by semiconductor substrates, substrates used for liquid crystal displays, magnetic substrates, and the like.
Examples of the oxidative gases include an ozone gas and oxygen gas. Examples of the reductive gases include a hydrogen gas or the like. Examples of inert gases include a helium gas, argon gas, krypton gas, xenon gas, neon gas, nitrogen gas and the like.
Deionized water is generally water (primary deionized water) produced by treating raw water in a primary deionized water production device comprising a coagulating sedimentation unit, sand filtration unit, active carbon filtration unit, reverse osmosis unit, two-bed ion exchange system, mixed-bed type ion exchange system, micronic filter unit and so forth.
In addition, generally high-purity water can be obtained by treating the above deionized water stored in a deionized water reservoir in a secondary deionized water production system comprising ultraviolet irradiation apparatus, mixed-bed type polisher and membrane separation unit such as ultrafiltration unit and reverse osmosis unit arranged in that order to remove residual impurities in the primary deionized water such as fine particles, colloidal materials, organic metals, and anions as much as possible, yielding high-purity water (secondary deionized water) suitable for wet treatment of objects to be rinsed. In a commonly used configuration, high-purity water (secondary deionized water) thus obtained is generally supplied to the points of use and any excessive high-purity water is returned (secondary deionized water) to the above-mentioned primary deionized water reservoir via a return line.
Water quality of high-purity water (secondary deionized water) is shown in table 1:
High-purity water (secondary deionized water) and the above-mentioned primary deionized water are collectively referred to as deionized water herein.
If a high-pressure cylinder gas is to be used as a gas supply source, the pressure of the gas supplied to deionized water may be controlled by a reducing valve.
If an oxidative gas (ozone gas) or reductive gas (hydrogen gas) is derived from a water electrolyzer, the pressure of such a gas supplied to deionized water may be controlled by controlling the pressure of water supplied to such electrolyzer: the pressure of the ozone gas or the hydrogen gas generated by way of the water electrolyzer is a function of the pressure of water supplied to such electrolyzer. Thus, the pressure of the ozone gas or the hydrogen gas generated can be adjusted to a desired value commensurate with a predetermined value of water supplied to the water electrolyzer. This may be accomplished by establishing the specific interrelationship between the pressure of a generated gas and that of supply water by preliminary experiment for each water electrolyzer.
The absolute pressure of a gas supplied to deionized water should preferably be not less than 1.0 kgf/cm2 (=9.8xc3x97104 Pa, hereinafter kgf/ cm2 is used for a pressure unit). When a gas is dissolved at such a pressure, a cleaning solution with particularly excellent detergency can be obtained. A pressure more than 5 kgf/cm2 is often meaningless, because a cleaning solution is usually used under the atmospheric pressure. Therefore, the preferable gas supply pressure is from 1 to 5 kgf/cm2.
The pressure of deionized water should preferably be not less than 1 kgf/cm2, and more preferably should range from 1 to 5 kgf/cm2.
In the preparation of the cleaning solution, degassing deionized water is preferably carried out before dissolving an oxidative gas, reductive gas, or inert gas or a mixture gas of an oxidative gas and an inert gas or a mixture of a reductive gas and an invert gas because the detergency of a cleaning solution (deionized water that have dissolved an oxidative gas, reductive gas, or inactive gas or a mixture of an oxidative gas and an inert gas or a mixture of a reductive gas and an inactive gas) thus prepared is more effective than that of cleaning solution not so prepared. Said degassing of deionized water is usually carried out using a vacuum degassing unit or a membrane-degassing unit.
It is preferable to dissolve a gas in deionized water by diffusing the gas in it through a gas permeable membrane unit.
It is another feature of the cleaning solution manufacturing device according to the present invention that the device comprises a deionized water supply source, a supply source of an oxidative gas, reductive gas, or an inert gas or a mixture gas of an oxidative gas and an inert gas or a mixture gas of a reductive gas and an inert gas, a gas-dissolving unit wherein a gas from said supply source is dissolved in deionized water from said deionized water supply source to supply gas-dissolved cleaning solution to objects to be cleaned, and a gas supply pressure controller wherein the pressure of a supplied gas is controlled at a value exceeding the atmospheric pressure when dissolving the gas in deionized water.
A cylinder gas itself, for example, may be used as a supply source of an oxidative gas, reductive gas, or inert gas, or a mixture gas of an oxidative or reductive gas and an inert gas. If an oxidative gas is an ozone gas and if a reductive gas is a hydrogen gas, a water electrolyzer may be used as the gas supply source.
It is preferable that the cleaning solution manufacturing device further comprises a degassing unit wherein deionized water from said deionized water supply source is degassed to supply deionized water degassed in the degassing unit to the gas-dissolving unit. The detergency of cleaning solution thus prepared can be enhanced by removing a nitrogen gas in the air normally dissolved in deionized water.
With reference to a gas supply pressure controller wherein the pressure of a supplied gas is controlled at a value exceeding the atmospheric pressure when dissolving the gas in deionized water, if a high-pressure cylinder gas is used as a gas supply source as mentioned above, a pressure reducing valve may be used. When a water electrolyzer is used as the gas supply source, a pressure controller (for example, a pressure Pump) may be used to control the pressure of deionized water supplied to the water electrolyzer.
The gas-dissolving unit is preferably a gas permeable membrane unit wherein a gas is diffused in deionized water through the membrane.
Since the concentration of a gas dissolved in deionized water is proportional to the supply pressure of the gas, the gas supply pressure can be controlled by detecting the gas concentration in deionized water. Based on this fact, the concentration of a gas dissolved in deionized water can be controlled to a desired level by installing a gas concentration detector unit wherein the concentration of the gas dissolved in deionized water is detected, and a control system wherein a gas supply pressure controller operates based on the signal from the gas concentration detector unit.